[dmd-internals] Memory Leak

[Iain Buclaw]

On 11 November 2012 07:28, Alex Rønne Petersen <xtzgzorex at gmail.com> wrote:
> On Sun, Nov 11, 2012 at 8:26 AM, David Held <dmd at wyntrmute.com> wrote:
>> While writing some unit tests for Dsymbol, I noticed that
>> Dsymbol::toPrettyChars() leaks almost everywhere.  In the simple case where
>> a symbol has no parent, it just returns toChars(), which does not leak (at
>> least I don't think it does).  However, whenever the symbol has a parent (or
>> many), the returned string is composed, which requires that it is allocated
>> dynamically (via mem.malloc()). Even though the caller owns the string, and
>> even though it is called dozens of times, it appears that none of the
>> callers are properly disposing of the result.  Unfortunately, it is a bit
>> messy to do so, because you must free the string *only* if it has a parent,
>> which is a pretty bad implementation leak, IMO.  Here is a place where
>> std::string would have worked nicely. ;)
>>
>> I suspect this has gone unnoticed because A) dmd probably has a relatively
>> small memory footprint to begin with or B) most invokations of
>> toPrettyChars() are during a call to error(), so the compiler is about to
>> quit anyway.  What to do?  Leave it alone?  Try to fix it?  Note that fixing
>> it without changing toPrettyChars() would require adding 2-3 lines of code
>> to almost every call.
>>
>> Dave
>>
>>
>> P.S.  Incidentally, this bug is one that is not easily caught with
>> assertions (where would you place the assert that the string was freed?).
>> Fortunately, it is caught by unit testing; but it could also have been
>> caught by documenting that the caller owns the string.  This is why you
>> really want all 3 approaches to code quality.
>
> DMD as a whole is written for garbage collection. It just so happens
> that it doesn't use one at the moment, which means a lot of things
> will leak.
>

Another thing that's on my todo list, scoping out integration of all
DFE types into GCC's GType system so that it works with the GCC GC.
:-)

So far, the only thing I've heard on the Linux side is strapping the
Boehm GC onto the frontend, IIRC the GC in DMD is for Windows only?

-- 
Iain Buclaw

*(p < e ? p++ : p) = (c & 0x0f) + '0';